Injection moulding tool and method for production thereof

ABSTRACT

An inventive method for the production of a metal mould in order to manufacture a limited amount of mass-produced injection moulded parts comprised of producing a moulded part by means of injected powder moulding based on a model for said injection moulded part and in producing a tool therefrom by means of debinding and sintering.

[0001] The invention relates to a method for the production of a metal injection moulding tool for the limited mass production of injection moulded parts with dimensions typically greater than 1 mm. For the purpose of this description, the expression “limited mass production” is used for the manufacture of injection moulded parts in runs preferably in the order of 1000 to 100,000. For comparison, conventional injection moulding tools allow runs of about ten times the size, whereas the so-called rapid tooling or rapid prototyping method is suitable for runs of about one tenth the size

[0002] Conventional injection moulding tools for the mass production of injection moulded parts are very laborious to produce and hence very expensive. This applies especially to finishing in cases where modifications are subsequently required, so they are only economic for the true mass production of millions of pieces.

[0003] Temporary tools made of diverse materials are therefore often used for the production of small numbers of prototypes or the production of pilot runs and small runs. Thus, for example, casting resin tools or even wooden moulds have already been in conventional use for a relatively long time in the casting mould or thermoforming technique.

[0004] Because of the high pressures in the tool, the injection moulding process has always meant that said temporary materials can only be used for a short time More recently, there has been a growing interest in tools which can be produced rapidly and inexpensively. The object of the invention is therefore to produce an injection moulding tool which on the one hand can be produced rapidly and inexpensively and on the other hand allows larger production runs than do tools made of “soft materials”.

[0005] This is achieved according to the invention by a method of the type mentioned at the outset which is characterized in that a model of the injection moulded part to be manufactured is placed in a standard casting mould, powder is injected into the mould with the model in position, and the moulded part formed is debound and then sintered.

[0006] An Example of the invention is described below with the aid of the attached drawings, in which:

[0007]FIG. 1 is a schematic representation of the steps of the method for the production of an injection moulding tool for the manufacture of a plastic cog, and

[0008]FIG. 2 is a detail of the production method.

[0009] A model 1 of the injection moulded part 2 to be manufactured—a plastic cog in the present case—can be produced in various ways. The extra amounts necessary to compensate for the shrinkage on sintering are known from injected powder moulding technology. In the present Example, a mould of the model is produced on the basis of CAD worksheets 3 by means of the known stereolithography 4 and the synthetic resin model 1 is cast in said mould in a casting process 5, also known per se.

[0010] In the next step, this model is placed or mounted in a standard casting mould 6. The mould is then closed and powder is injected into it. The resulting moulded part 7 constitutes a so-called green body and in this state is very easy to work.

[0011] The next step is the debinding of the moulded part, which can be carried out in various ways, e.g. by thermal decomposition, solvent extraction, catalytic debinding, etc. The final step is sintering, i.e. pressureless compaction of the moulded part, to reach approximately the theoretical density of the metallic material. The result is a metal injection moulding tool 8 which allows the manufacture of injection moulded parts in runs in the order of 100,000.

[0012] The advantages of this method are firstly the relatively short time required from the design drawing to the finished tool, a typical duration being no more than two weeks. Secondly, the method is extremely inexpensive. A tool produced by this method is about 20 to 30% of the cost of a conventional production tool. Finally, a further advantage is the possibility, illustrated in FIG. 2, of producing several identical moulded parts 9, 10, 11 and keeping them in the green body state. Because they can easily be finished in this state, they can be modified very rapidly as required. Thus the tool retouching operations, modifications or repairs feared in conventional injection moulding technology no longer present a problem.

[0013] The material used for the tool is preferably steel, but it is also conceivable to use other materials, e.g. ceramic, which can be processed by injected powder moulding. 

1. Method for the production of a metal injection mould for the limited mass production of injection moulded parts with dimensions typically greater than 1 mm, characterized in that: (a) a model of the injection moulded part to be manufactured is placed in a standard casting mould, (b) powder is injected into the mould with the model in position, (c) the moulded part formed is debound and (d) the debound moulded part is sintered.
 2. Method for the production of an injection mould according to claim 1, characterized in that the moulded part is finished prior to debinding.
 3. Method for the production of an injection mould according to claim 1, characterized in that the model is produced by the so-called rapid prototyping method, e.g. by means of stereolithography.
 4. Metal injection mould for the limited mass production of injection moulded parts, characterized in that it is produced by a method according to one of claims 1-3.
 5. Application of the injected powder moulding method to the production of a metal injection mould for the limited mass production of injection moulded parts. 